Process and installation for covering a surface of a substrate with a layer of a fluid material

ABSTRACT

Process for covering a surface ( 1   a ) of a substrate ( 1 ) with a layer ( 2 ) of a fluid material, characterized in that: (a) with a confining wall ( 3 ) closed up on itself, arranged some distance from and above the surface to be covered ( 1   a ), and whose lower edge ( 3   a ) forms together with the latter a peripheral void ( 4 ), is defined a treatment chamber ( 5 ) delimiting an area ( 6 ) to be treated on the said surface to be covered; (b) a controlled vacuum is established inside the treatment chamber ( 5 ) by admitting an incoming gas stream ( 7 ) via the peripheral void ( 4 ), and by extracting an outgoing gas stream ( 8 ) from the treatment chamber, so as to obtain an internal pressure in the said chamber which is lower than the external pressure; (c) a controlled fluid stream ( 10 ) is introduced into the treatment chamber ( 5 ) under vacuum, this stream comprising the fluid covering material, which forms at the level of the peripheral void, together with the incoming gas stream ( 7 ), a turbulent mixed flow, which is aspirated into contact with the developed surface ( 1   b ) in the area ( 6 ) to be treated, depositing the fluid material thereat, and which is then discharged with the outgoing gas stream ( 8 ).

This is a National Stage Application of PCT/IB97/01608 filed Dec. 30,1997.

The present invention relates to the covering of a surface of asubstrate with a layer of a fluid material, or the depositing on thesaid surface of a continuous layer of the said fluid material.

BACKGROUND OF THE INVENTION

Various solutions have already been proposed in the prior art, forcovering a surface of a substrate, in relative motion or otherwise, witha fluid material (liquid or powder for example).

All the proposed solutions have in common on the one hand the priorformation, by overpressure or under vacuum, of a turbulent mixed flowobtained by mixing, with entrainment if necessary, of a controlled fluidstream comprising the fluid covering material, and of a gas stream, andon the other hand various arrangements making it possible to recover theunused or unconsumed turbulent mixed flow so as to avoid its diffusioninto the ambient air.

In accordance with document WO-92/12803, and in particular according tothe embodiment described with reference to FIGS. 22 to 24, and from line11 of page 27 to line 33 of page 29, there is described an installationfor covering the surface of a substrate 643 with a fluid material.

This installation comprises a means of treatment comprising a confiningwall 657, with an edge defining the area to be treated. A means 666makes it possible to establish a controlled vacuum inside the area to betreated, by admitting several incoming gas streams 684 and 680, throughthe aforesaid void. A means of controlled introduction, or head 642,into the area to be treated of the fluid material 644, associates acontrolled flow void with a pressurized air inlet 645/446, so that aturbulent mixed flow 682/683, circulating in contact with the substrate643, is produced directly at the head outlet; cf. page 27, lines 14 to21.

The incoming air streams 684 and 680 are all formed only so as tocontain the turbulent mixed flow in the area to be treated; cf. forexample page 29, lines 1 to 4, and lines 25 to 30.

In accordance with document WO-79/00469, a turbulent mixed flow isobtained by previously mixing a controlled fluid stream (3) comprisingthe fluid covering material, and a gas stream, these two streams beingunder overpressure so as to eject the mixed flow through a distributionvessel (5). Two successive confining walls of cylindrical shape form twoconcentric peripheral volumes 6 and 7, under vacuum, so as to dischargethe turbulent mixed flow after its contact with the surface to becovered.

In accordance with document GB-1 134 069, a turbulent mixed flow isobtained, under vacuum, by mixing a fluid stream (powder) and a gasstream. The turbulent mixed flow resulting from this circulates as aco-current, still under vacuum, in contact with the surface of anelongate substrate moving translationally.

In accordance with document WO-96/09122, a nozzle for spraying a powderis described, making it possible to eject under pressure a turbulentmixed flow obtained previously by mixing a fluid stream (powder) and agas stream. The unused mixed flow is reaspirated around the nozzle byappropriate means.

At the conclusion of this examination, all the prior solutions have thecommon characteristic of pushing as it were the fluid material onto thesurface of the substrate to be covered. This characteristic may prove tobe inefficient for covering substrates with an irregular surface, forexample a porous surface.

SUMMARY OF THE INVENTION

In accordance with the present invention, consideration is thereforegiven to any substrate or support, whose apparent surface area issmaller in value than the actual or developed surface area of the samesubstrate, by reason of the presence of asperities, bumps, or surfacepores, generating a larger developed surface area than the apparentarea, that is to say that visible to the naked eye.

The subject of the present invention is a process and an installationfor covering a surface such as defined above, and doing so by attractingas it were the fluid covering material towards and into the entiresurface of the substrate.

The process in accordance with the present invention associates incooperation the following steps:

(a) with a confining wall closed up on itself, arranged some distancefrom and above the surface to be covered, and whose lower edge formstogether with the latter a peripheral void, a treatment chamberdelimiting on the surface to be covered an area to be treated is definedor made available

(b) a controlled vacuum is established inside the treatment chamber byadmitting an incoming gas stream via the peripheral void, and byextracting an outgoing gas stream from the treatment chamber, so as toobtain in the said chamber an internal pressure which is lower than theexternal pressure, that is to say outside the same chamber

(c) a controlled fluid stream is introduced into the treatment chamberunder vacuum, this stream comprising the fluid covering material, whichforms at the level of the peripheral void, together with the incominggas stream, a turbulent mixed flow, which is aspirated into contact withthe developed surface in the area to be treated, depositing the fluidmaterial in the latter; then this mixed flow is discharged with theoutgoing gas stream.

An installation for implementing the process described above comprises,in a general manner:

a means of treatment, comprising a confining wall closed up on itself,designed so as to be arranged some distance from and above the surfaceto be covered, with a lower edge adapted or designed so as to formtogether with the said surface to be covered a peripheral void; thisconfining wall defines a treatment chamber delimiting an area to betreated on the said surface to be covered

means for establishing a controlled vacuum inside the treatment chamberby admitting an incoming gas stream through the peripheral void, and byextracting an outgoing gas stream from the treatment chamber, so as toobtain an internal pressure in the said chamber which is lower than theexternal pressure, that is to say outside the said chamber

a means of controlled introduction into the treatment chamber, undervacuum, of a fluid stream comprising the fluid covering material, so asto form, at the level of the peripheral void, with the incoming gasstream a turbulent mixed flow, which is aspirated into contact with theentire developed surface in the area to be treated, depositing the fluidmaterial thereat; this mixed flow is then discharged with the outgoinggas stream.

The term “fluid material” should be understood to mean any product,substance or material, in the liquid, fluid or viscous state, which canbe dispersed by the incoming gas stream in the treatment chamber, so asto form with the latter a turbulent, mixed flow, that is to say onecomposed of particles of the said fluid material in suspension in thisincoming gas stream, doing so under the predetermined conditions,especially of temperature, adopted for treating the surface to becovered with the said fluid material. As an example of a fluid materialof this kind may be cited any paint, comprising pigments or dyes insuspension or solution in an appropriate liquid medium, or else anymaterial in the substantially solid or solid state under the normal orambient conditions of temperature, but liquid or liquefied at thetemperature for treating the surface, the covering obtained subsequentlysolidifying on the surface of the substrate; in this latter case may becited for example any heavy hydrocarbon, for example a paraffin.

The term “fluid stream” should be understood to mean any liquid, fluid,viscous or pasty flow or stream which can be dispersed by the incominggas stream in the treatment chamber, under the conditions, especially oftemperature, adopted or predetermined for the operation of the treatmentchamber.

By virtue of the process and the installation according to the presentinvention, the treatment or covering of the surface of the treatedsubstrate is performed as close as possible to the latter, withoutspraying the fluid material adopted for coating the said surface to theoutside or towards the outside.

The invention as defined above is distinguished from each documentintroduced earlier by way of prior art through the existence of aperipheral void defined between the lower edge of the confining wall andthe surface to be covered, at the level of which the controlled stream(fluid covering material) is introduced into the incoming gas streamthrough the said void, and consequently at the level of which theturbulent mixed flow necessary for covering the said surface isobtained.

This fundamental difference makes it possible to supply the fluidcovering material in a dynamic manner and as close as possible to thesurface to be covered.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is now described with reference to the appendeddrawing in which:

FIG. 1 represents, diagrammatically, an installation in accordance withthe present invention,

FIG. 2 represents, still diagrammatically, a treatment means or head,belonging to the installation represented in FIG. 1

FIG. 3 represents, on an enlarged scale, a substrate, such as treated orcovered according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An installation according to the invention comprises in a generalmanner:

a treatment means or head 14, which can move with respect to the surfacela of the substrate 1 to be covered or coated, and is designed to bemanipulated by the user; this means comprises principally a confiningwall 3, closed up on itself, having for example symmetry of revolution,defining a treatment chamber 5 which delimits in opposite relationthereto an area 6 to be treated of the surface to be covered 1 a

means 13 for establishing a controlled vacuum inside the treatmentchamber 5

a means 16 of controlled introduction into the treatment chamber, undervacuum, of a fluid stream 10 comprising the fluid covering material

a means of separation 17 making it possible to obtain a gas stream 18and a fluid stream 19

a means 30 of recycling the fluid stream towards the means 16 ofcontrolled introduction

and another means of recycling the gas stream 18, identical to the means13 of controlled vacuum.

The treatment means or head 14, more particularly represented in FIG. 2,exhibits in general a symmetry of revolution about an axis, andgenerally has the shape of a bell for example. This means 14 comprises,from the outside to the inside, an external wall 11, closed up onitself, a confining wall 3, likewise closed up on itself, separated fromthe external wall, and delimiting with the latter an annular passage 12,and an internal wall 20, arranged some distance from the confining wall3, but sufficiently near to the latter to form a cylindrical capillarychannel, terminating in a calibrated orifice 9, thus forming a means ofcontrolled introduction 16, under the control of the pressure differenceexisting between the upstream and the downstream of the said orifice.The treatment chamber 5 is delimited inside the confining wall 3, andmore exactly inside the internal wall 20. By construction, the loweredge 11 a of the external wall 11 lies below the lower edge 3 a of theconfining wall 3, so that a peripheral void 4 is formed between thelower edge 3 a and the surface 1 a of the substrate to be treated,during the implementation or use of the means of treatment or head 14.The lower edge 11 a of the external wall 11 is equipped with rollingmeans 21, such as rollers, thereby making it possible to ensurefrictionless movement of the treatment head or means 14, over the wholesurface la of the substrate 1. These rollers are arranged in such a wayas to form, between the lower edge Ha and the surface 1 a to be covered,a passage for the leakage of ambient air to the inside of the treatmenthead 14.

This treatment means or head 14 is linked to the other components of theinstallation, as follows:

the annular passage 12 communicates via a pipe 22 with the output of themeans 13 of controlled vacuum, or pump, which recycles the gas stream 18obtained at the outlet of the means of separation 17 to the annularpassage 12, to constitute the incoming gas stream 7, passing in acalibrated manner into the peripheral void 4

via a pipe 23, passing in a sealed manner into the pipe 22, the outletof the treatment chamber 5 communicates with the inlet of the means ofseparation 17, for discharging the outgoing gas stream 8 from the saidchamber

the capillary cylindrical channel, terminating in the calibrated orifice9, communicates via a pipe 24 with an intermediate reserve 25 of fluidmaterial, itself linked to the output of a pump 30.

The means 13, or pump, makes it possible to ensure the recycling of thegas stream 18 exiting the means of separation 17, in the guise of a gasstream 7 entering the treatment chamber 5. Also, this same means 13, byaspiration of the pump, makes it possible to establish a controlledvacuum inside the chamber 5, by way of the means of separation 17. Thiscontrolled vacuum is the result, on one side of the gas stream 7entering in a controlled manner through the peripheral void 4, and ofthe outgoing gas stream 8 extracted from the treatment chamber 5 via thepipe 23, the whole so as to obtain in the chamber 5 an internal pressurewhich is lower than the external pressure, that is to say than thatprevailing in the annular passage 12.

The means of controlled introduction 16 is identified with thecalibrated orifice 9, allowing through the fluid stream 10, when thedifference in pressure between the upstream and the downstream of thisorifice is greater than the loss of head of the latter in relation tothe same fluid stream 10. During operation, the means of controlledintroduction is therefore under the control of the vacuum prevailing inthe chamber 5, and consequently of the internal pressure in the latter,in conjunction with the external pressure in the annular passage 12.

The means of separation of tank 17 is linked by the pipe 23 to theoutlet of the treatment chamber 5. This means makes it possible toseparate the mixed flow gathered, on the one hand into a fluid stream 19recycled by the pump 30 to the intermediate storage container 25, and onthe other hand into a gas stream 18 recycled by the pump 13 to theannular passage 12 of the means of treatment or head 14.

During operation, the means of treatment or head 14 is arranged abovebut nevertheless some distance from the surface 1 a of the substrate 1to be covered, and defines an area 6 of the latter to be treated, whichmoves around the entire surface of the substrate, as a function of themanual displacement for example of the means of treatment or head 14.

By starting the pump 13 a controlled vacuum is established inside thetreatment chamber 5 so that an internal pressure which is lower than theexternal pressure in the annular passage 12 is established in the saidchamber.

Under the effect of the vacuum existing in the chamber 5 a controlledfluid stream 10 is introduced, at the level of the peripheral void 4,into the treatment chamber 5. This fluid stream 10 comprises the fluidcovering material, and forms together with the incoming gas stream 7 aturbulent mixed flow which is aspirated into contact with the developedsurface 1 b in the area 6 to be treated (cf. FIG. 3). It is thisturbulent mixed flow which deposits the fluid material in all theasperities, bumps and pores of the surface of the substrate 1, and thenthis mixed flow is discharged from the chamber 5 with the outgoing gasstream 8.

The residual turbulent mixed flow introduced into the means ofseparation 17 is separated into a liquid stream recycled to theintermediate container 25 and a gas stream 18 recycled by the pump 13 tothe annular passage 12 of the means of treatment or head 14.

In total, uniform, even and continuous coverage 2 is obtained over theentire developed surface 1 b of the substrate 1, as shown in FIG. 3.

What is claimed is:
 1. Process for covering a surface (1 a) of asubstrate (1) with a layer (2) of a fluid material, according to which:(a) with a confining wall (3) closed up on itself, arranged somedistance from and above the surface to be covered (1 a), and whose loweredge (3 a) forms together with the latter a peripheral void (4), isdefined a treatment chamber (5) delimiting an area (6) to be treated onthe said surface to be covered (b) a controlled vacuum is establishedinside the treatment chamber (5) by admitting an incoming gas stream (7)via the peripheral void (4), and by extracting an outgoing gas stream(8) from the treatment chamber, so as to obtain an internal pressure inthe said chamber which is lower than the external pressure (c) aturbulent mixed flow between a fluid stream (10), comprising the fluidcovering material, and a gas stream, is formed in the treatment chamber(5) under vacuum, the said turbulent mixed flow coming into contact withthe developed surface (1 b) in the area (6) to be treated, depositingthe fluid material thereat, and then being discharged with the outgoinggas stream (8) characterized in that the fluid stream (10) is introducedin a controlled manner at the level of the peripheral void (4), betweenthe lower edge (3 a ) of the confining wall (3) and the surface to becovered (1 a), the said controlled fluid stream forming, together withthe gas stream (7) entering via the said void, the turbulent mixed flow,which is aspirated into contact with the developed surface (1 b) in thearea (6) to be treated.
 2. Process according to claim 1, characterizedin that the fluid stream (10) introduced (7) into the treatment chamber(5) is controlled by a calibrated orifice (9), allowing through the saidfluid stream when the difference in pressure between the upstream andthe downstream of the said orifice is greater than the loss of head ofthe said orifice in relation to the said fluid stream.
 3. Processaccording to claim 1, characterized in that, with another external wall(11), closed up on itself, separated from the confining wall (3), apassage (12) for the incoming gas stream (7) is delimited with thislatter wall through the peripheral void (4) between the lower edge (3 a) of the confining wall (3) and the surface to be covered (1 a). 4.Installation for covering the surface (1 a) of a substrate (1) with alayer (2) of a fluid material, comprising: a means (14) of treatment,comprising a confining wall (3) closed up on itself, designed so as tobe arranged some distance from and above the surface to be covered (1a), with a lower edge (3 a ) adapted so as to form together with thelatter a peripheral void (4), the said confining wall defining atreatment chamber (5) delimiting an area (6) to be treated on the saidsurface to be covered a means (13) for establishing a controlled vacuuminside the treatment chamber (5) by admitting an incoming gas stream (7)through the peripheral void (4), and by extracting an outgoing gasstream (8) from the treatment chamber, so as to obtain an internalpressure in the said chamber which is lower than the external pressure ameans of forming, in the treatment chamber (5) under vacuum, a turbulentmixed flow between a fluid stream (10), comprising the fluid coveringmaterial, and a gas stream, the said turbulent mixed flow coming intocontact with the developed surface (1 b) in the area (6) to be treated,depositing the fluid material thereat, and then being discharged withthe outgoing stream (8) characterized in that the means of forming theturbulent mixed flow is a means of controlled introduction (16) of thefluid stream (10), arranged at the level of the peripheral void (4)between the lower edge (3 a ) of the confining wall (3) and the surfaceto be covered (1 a), the said controlled fluid stream forming, togetherwith the gas stream entering by the said void, the turbulent mixed flow,which is aspirated into contact with the developed surface (1 b) in thearea (6) to be treated.
 5. Installation according to claim 4,characterized in that the means of controlled introduction (16) of thefluid stream comprise a calibrated orifice (9), allowing through thefluid stream when the difference in pressure between the upstream andthe downstream of the said orifice is greater than the loss of head ofthe said orifice in relation to the said fluid stream.
 6. Installationaccording to claim 4, characterized in that the means of treatment (14)comprises another wall (11), external, closed up on itself, separatedfrom the confining wall (3), delimiting with the latter a passage (12)for the incoming gas stream through the peripheral void (4) between thelower edge (3 a) of the confining wall (3) the surface to be covered (1a).
 7. Installation according to claim 4, characterized in that itcomprises: a means (17) of separating the mixed flow into a gas stream(18) and a fluid stream (19) a means (30) of recycling the fluid streamtowards the means of controlled introduction (16) another means ofrecycling (13) the gas stream (18) in the form of an incoming gas stream(7), the said means of recycling the gas stream also being the means ofproviding the controlled vacuum.